AB copolymer dispersants are known in the art and are used to form pigment dispersions that are used in a variety of coating compositions and for inks, in particular for inks for ink jet printers. U.S. Pat. No. 4,656,226 issued Apr. 7, 1987, to Hutchins et al shows an AB block copolymer dispersant having polar groups such as acid or amine groups that attach to a pigment's surface and the other block of the polymer keeps the pigments stabile in the dispersion or coating composition. U.S. Pat. No. 5,231,131 to Chu et al issued Jul. 27, 1993 shows the use of graft copolymers to form aqueous pigment dispersions. U.S. Pat. No. 5,272,201 issued Dec. 21, 1993 to Ma et al and U.S. Pat. No. 5,221,334 issued Jun. 22, 1994, to Ma et al show AB or BAB block polymers that are used in aqueous printing inks to keep pigments dispersed in the inks.
A number of the above polymer dispersants are made via group transfer polymerization (GTP). GTP is a "Living" free radical polymerization technique and is a well-known technique that is used to form the aforementioned block polymers. In GTP, an initiator splits with one end going to the tail of an acrylic monomer unit and the other to the head. The group at the head transfers to the head of a second monomer unit as that unit is polymerized with the first. Such techniques are described in U.S. Pat. Nos. 4,417,034 issued Nov. 22, 1983, and 4,508,880 issued Apr. 2, 1985, to O. W. Webster and U.S. Pat. Nos. 4,414,372 issued Nov. 8, 1983, and 4,524,196 issued Jun. 18, 1985 to Farnham et al. The above patents are hereby incorporated by reference.
Conventional truck and automobile finishes comprise a clear coat applied over a pigmented base coat that is applied over a primer layer. The polymer dispersant used in the base coat must not only keep the pigment dispersed but needs to contain a reactive group that will react with the crosslinking agent used in the coating composition which on curing makes the dispersant an integral part of the resulting finish. Polymer dispersants can cause intercoat adhesion failures and usually are used only in limited amounts. It is desirable that the polymer dispersant have reactive groups that will bond with the primer layer to improve intercoat adhesion of the base coat to the primer rather than cause intercoat adhesion problems that cause flaking and chipping of the resulting finish. Carbon black pigments are particularly difficult to disperse and a dispersant is needed that disperses the carbon black pigment but also has the above properties.